Hydrology

Tile drainage: Promotes more infiltration, slowing water delivery from the landscape (compared to surface drainage). However, studies indicate potential for overall water yield increases from 5 to 10 percent.

The percentage of tile-drained land in Minnesota widely varies, but perhaps 20 to 30 percent of the agricultural soils in the Minnesota River Basin are tile-drained. In some locations, higher percentages exist (Figure 2).

Minnesota farmers can drain their lands, provided they have an outlet and comply with Department of Agriculture and state wetland regulations (Figure 3).

Current drainage activity in the Midwest typically replaces older, less effective drainage systems with new systems. In these new systems, it’s important to incorporate technologies to reduce environmental concerns (Figure 4).

Figure 2: Minnesota has more than 21,000 miles of ditches and channelized streams (in red) that serve as the drainage infrastructure for agricultural regions. Source: Minnesota Department of Natural R

Figure 5: Installation of drainage water management system with control structures. Photo: Brad Carlson

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Drainage water management design (Figures 6 and 7) calls for dividing the field into water control/management zones, aligning laterals with the field contours and using control structures. Annual subsurface flow and nitrate reductions of 10 to 50 percent may be possible.